Influence of Fe-rich intermetallic inclusions on pit initiation on aluminum alloys in aerated NaCl

Journal Article · Mon Feb 01 04:00:00 EST 1999 · Journal of the Electrochemical Society

DOI:https://doi.org/10.1149/1.1391637· OSTI ID:328209

Park, J O; Paik, C H; Huang, Y H; Alkire, R C ^[1]

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1. Univ. of Illinois, Urbana, IL (United States)

The role that Al{sub 3}Fe intermetallic inclusions play during initiation of pitting corrosion on aluminum alloys was investigated in 0.6 M NaCl. In aerated solutions microscopic observations showed the growth of cavities in the host metal adjacent to inclusions. The rest potential of synthetic Al{sub 3}Fe was measured in aerated and deaerated NaCl solutions over a range of bulk pH values between 2 and 12 and was found to act as a cathode. In aerated solutions rotating disk electrode experiments on synthetic Al{sub 3}Fe electrodes verified that the cathodic reaction corresponded to the reduction of dissolved oxygen. With scanning pH microelectrodes, measurements were carried out near synthetic Al{sub 3}Fe electrodes which were coupled in a galvanic cell with Al-6061 in NaCl solution. In addition, the pH measured over Al-6061 at a distance of 25--30 {micro}m from the surface was observed to fluctuate between pH 4 and 8.5 for the first 2 h of immersion in NaCl solutions. Atomic force microscopy images of Al-6061 immersed in buffered aerated 0.6 M NaCl solution (pH 5.5) did not show any evidence of dissolution of the Al around intermetallics. These measurements support the view that Al{sub 3}Fe particles in Al-6061 serve as local cathodes, that a high pH develops around the intermetallic particles by dissolving alkaline cavities to evolve into a small number of rapidly dissolving acidic pits.

• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: FG02-91ER45439
• OSTI ID: 328209
• Journal Information: Journal of the Electrochemical Society, Journal Name: Journal of the Electrochemical Society Journal Issue: 2 Vol. 146; ISSN 0013-4651; ISSN JESOAN
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM BASE ALLOYS
INCLUSIONS
INTERMETALLIC COMPOUNDS
IRON ALLOYS
PITTING CORROSION
SODIUM CHLORIDES